The present invention relates to a method for drawing sheet metal components made of sheet bars in a drawing tool which has an upper tool and a lower tool and is drivable in a stroke-executing fashion by a press, in which a sheet bar is removed from a supporting surface and, with the drawing tool opened, placed in a positionally defined fashion on a bearing face of the lower tool. The drawing tool is closed with the application of force and the drawn sheet metal component is subsequently removed from the re-opened drawing tool. The present invention also relates to a device for inserting sheet bars into a drawing tool, the drawing tool containing a die-plate, a drawing punch and a drawing frame, with an upper component of the drawing tool being drivable in a stroke-executing fashion, the drawing tool also containing bearing faces, with an upper bearing face assigned to the upper tool and a lower bearing face assigned to a lower tool, the upper and lower bearing faces together clamping in the sheet bar during drawing. The device includes a sheet bar inserter which has a program-controllable working arm with a gripper attached to an outer end of the working arm, the gripper having a plurality of controllable adhesion elements that are at least one of suction cups and electromagnets that pick up or set down a sheet bar, the adhesion elements being mutually spaced with respect to one another.
German Patent Document 40 02 324 shows a known method and device for inserting sheet bars into drawing tools, and has a gripper with a plurality of controllable suction cups for removing flat oiled sheet bars from a stack of sheet bars and subsequently inserting the removed sheet bars into a deep-drawing tool. Because of the oiling of the sheet bars in order to improve their sliding capacity and deep-drawing capacity, the sheet bars may stick to one another in the stack so that problems may result when removing them individually. By means of gripper-integrated, centrally arranged compression springs, the sheet bar to be removed should initially still be pressed against the stack of sheet bars in the central region using the known gripper and only lifted up in the corner region where the suction cups are arranged in order to ensure that the sheet bars are released and detached reliably. Even though the associated deep-drawing tool is not illustrated or described in greater detail in the aforesaid publication, cooperation between such a removal and detachment device with a deep-drawing press and the drawing tool attached therein can be assumed as known. It is disadvantageous on the known device that the gripped sheet bar which is to be inserted is forcibly pressed into a sagging shape by the action of the compression springs, which shape can spring up in an uncontrolled fashion after the transfer of the sheet bar to the deep-drawing tool. As a result, an exactly reproducible, accurately positioned insertion of the sheet bars into the deep-drawing tool cannot be ensured. This applies all the more for deep-drawing tools in which, as a result of drawing components, complicated bearing faces are present on the bearing frame. As a result of inaccurate depositing of the sheet bars in the deep-drawing tool and/or of uncontrolled movements of the sheet bar itself in the time between the release from the gripper and the closing of the tool, poor drawn component quality, and in an extreme case, rejects can result.
An object of the present invention is to improve the deep-drawing method of the initially described type and the insertion device of the initially described type for sheet bars so that, in particular in the case of complicated bearing faces of the deep-drawing tool, a uniformly high drawn component quality is achieved and rejects due to any kind of displacement of the sheet bars within the drawing tool as it closes are avoided.
This and other objects are achieved by the present invention which provides a method for drawing sheet metal components made of sheet bars in a drawing tool which has an upper tool and a lower tool and is drivable in a stroke-executing fashion by a press. The method comprises removing a sheet bar from a supporting surface, and with the drawing tool opened, placing the sheet bar in a positionally defined fashion on a bearing face of the lower tool. The sheet bar is preformed at least one of before and during the placement of the sheet bar on the bearing face into a shape which approximates the shape of the bearing face. The preformed sheet bar is secured on the bearing face until a closing of the drawing tool, the securing of the sheet bar on the bearing face being by at least one of the weight of the sheet bar, tool-integrated adhesion elements, and retaining elements. The drawing tool is closed with the application of force and then re-opened. The drawn sheet metal component is subsequently removed from the re-opened drawing tool.
The objects are also achieved by an embodiment of the present invention which provides a device for inserting sheet bars into a drawing tool, the drawing tool containing a die-plate, a drawing punch and a drawing frame, with an upper component of the drawing tool being drivable in a stroke-executing fashion, the drawing tool also containing bearing faces, with an upper bearing face assigned to the upper tool and a lower bearing face assigned to a lower tool, the upper and lower bearing faces together clamping in the sheet bar during drawing. The device comprises a sheet bar inserter which has a program-controllable working arm with a gripper attached to an outer end of the working arm. The gripper has a plurality of controllable adhesion elements that are at least one of suction cups and electromagnets that pick up or set down a sheet bar, the adhesion elements being mutually spaced with respect to one another. The gripper is a multi-legged gripping spider with which the picked-up sheet bar can be preformed in a defined manner during transportation from a picking-up location to the drawing tool and matched to a shape of the bearing faces. The gripper has a central body and legs that are pivotably attached to the central body and are placeable in a predetermined basic position in relation to the central body. The adhesion elements are pivotably coupled to an outer end of the legs. The legs have an effective length, corresponding to a distance from a coupling of the legs to the central body to the adhesion elements, that is controllably variable.
By means of forced elastic preforming, approximated to the shape of the bearing face, of the sheet bar which has been picked up already before insertion, this said sheet bar can be inserted quickly and securely even with complicated bearing faces and can be securely fixed to the lower bearing face by adhesion means integrated there so that the sheet bar which has been inserted in a preformed state cannot "jump up" afterwards until the drawing tool is closed. By virtue of the fixing by adhesion elements during the closing of the tool the inserted sheet bars cannot carry out any uncontrolled movements themselves. The sheet bar is consequently clamped in a controlled and exactly reproducible fashion between the two bearing faces of the lower tool and upper tool. As a result, a continuously high drawn component quality is achieved with the insertion of the sheet bars according to the invention and rejects due to possible displacement of the sheet bars within the drawing tool as it closes are avoided.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.